Hi eGlobal Auction,
It is actually not currently possible to associate listings that are already active on eBay with inventory items within your Auctiva account. In order to associate an eBay listing with an inventory item, you must check the "box next to "Is this an inventory item?" while creating the listing through Auctiva.
Any additional questions or concerns? Please feel free to contact our customer support team using the appropriate link on out help page: http://www.auctiva.com/free-auction-software-help/help.aspx
-Mike